ci cabal smoke test should include some info from the failure

[aryairani]

Currently when the CI cabal smoke test fails, it adds a comment to the PR that says something like.

Some tests with 'continue-on-error: true' have failed:

Cabal / smoke-test
Created by [continue-on-error-comment](https://github.com/mainmatter/continue-on-error-comment/?rgh-link-date=2026-02-05T18%3A34%3A54Z)

The actual error was:

Resolving dependencies...
Error: [Cabal-7107]
Could not resolve dependencies:
[__0] trying: unison-cli-0.0.0 (user goal)
[__1] unknown package: unison-util-diff3 (dependency of unison-cli)
[__1] fail (backjumping, conflict set: unison-cli, unison-util-diff3)
After searching the rest of the dependency tree exhaustively, these were the goals I've had most trouble fulfilling: unison-cli, unison-util-diff3

but it's buried under a pile of green checkmarks which makes it hard to spot.

It would be better to show this in the PR comment instead of the generic error if possible.